From my understanding, a hold means they're delaying making a decision on your application to see if they have space, and a waitlist means that you're not their first choice but they'll take you if their first choices don't matriculate. I think a hold is better than a waitlist -- it's kind of like a "pre-waitlist" -- meaning they want to accept you but aren't sure they have the space. At least this is how a school that put me on "hold" made it sound. They said "we do have a waitlist, and this is not it" (meant to be encouraging).